As a conventional method for the preparation of conductive metal nano-particles consisting of metal nano-particles having a particle size of not more than 100 nm, there has been known, for instance, a method comprising the step of reducing ions of a precious metal or copper to thus form a colloidal dispersion of the precious metal or copper (see, for instance, Patent Article 1 specified later). There has also been known a metal colloidal dispersion containing a compound having at least one amino group and at least one carboxyl group (see, for instance, Patent Article 2 specified below). In either of these methods, however, it has been quite difficult to prepare a stable metal colloid dispersion having a high concentration.
Patent Article 1: Japanese Un-Examined Patent Publication Hei 11-319538 (refer to Claims);
Patent Article 2: Japanese Un-Examined Patent Publication 2002-245854 (refer to Claims).